Far-infrared spectroscopy has been applied to the study of liquid phase molecular dynamics and interactions. The absorption and dispersion spectra of solutions of acetonitrile in carbon tetrachloride, across a range of temperatures and concentrations, have been obtained. These spectra have bean interpreted with the parameters obtained from a model developed from a generalised Langsvin equation of motion which includes intermolecular torque terms. The results obtained from the model analysis have been applied in an investigation of the non-reorientational contributions to the Raman and infrared bands arising from the and v(^1) and v(_3) modes. This study has shown that contrary to the assumptions commonly made, these contributions are not equal and some possible explanations for the discrepancies are given. A number of internal field theories are discussed and have been applied to the acetonitrile systems. The interpretation of the results of this analysis in terms of a simple model suggest that there is a preferred i.e. non-random orientation of the acetonitrile molecules in solution. A study of some tertiary alkyl ammonium halide solutions has revealed that there is a series of systems which separate into two liquid phases. Further investigation has highlighted the role of small amounts of water in these systems.